Hydrocarbon streams, such as oil sands, crude oils, asphalt, bitumens, etc. typically carry varying amounts of solids within the hydrocarbon stream. Excessive inorganic or organic solids in hydrocarbon streams negatively affect hydrocarbon processing by exacerbating fouling in heat exchangers, stabilizing emulsion in desalters, as well as reducing the value of hydrocarbon products. Oil sand contains a high amount of solids which complicates oil recovery. In addition, solids can clog burners, plug catalyst feed channels and deactivate catalysts. In heat exchangers heavy crude components (e.g. asphaltene) adsorb onto solids causing them to attach onto the tube surface. The adsorbed solids provide a nucleating growth site for the foulant. In a desalter, solids adsorb onto the water/oil interface, preventing electrocoalescence within the electrodes of the desalter. Solids can also reside at the effluent water/oil interface at the bottom of a desalter and prevent coalesced water droplets from immersing into the effluent water. This creates a rag layer that is detrimental in the desalting operation.
One option for removing the non-petroleum material is to first mix the raw product with water. For example, a water extraction process can be used to separate a majority of the non-petroleum material from the desired raw crude or bitumen. A water extraction process can remove a large proportion of the solid, non-petroleum material in the raw product. However, after the initial water extraction process, smaller particles of non-petroleum particulate solids will typically remain with the oil phase at the top of the mixture. This top oil phase is sometimes referred to as a froth. Separation of the smaller non-petroleum particulate solids can be achieved by adding an additional solvent to the froth of the aqueous mixture. This is referred to as a “froth treatment”. For example, a paraffinic solvent such as heptane can be added to the froth to cause a phase separation between an aqueous based phase and a bitumen phase. Unfortunately, due to the nature of the paraffinic solvent, a portion of the potential petroleum product is lost with the aqueous phase. The petroleum product lost with the aqueous phase may include a substantial portion of asphaltenes.
As an alternative to a water extraction, a non-aqueous extraction can be performed to separate crude oil from oil sands. Use of a non-aqueous extraction solvent can reduce or minimize the amount of water needed for extraction of crude oil from oil sands, and can potentially eliminate the need to perform a subsequent froth treatment. However, use of a non-aqueous extraction solvent can increase the amount of fine particulate matter that remains in the bitumen phase. The presence of an elevated content of fine particulate matter can create difficulties when attempting to transport such a non-aqueous extracted crude oil via pipeline.
Electrofiltration techniques have been proposed and studied for removal of solids from hydrocarbon liquids. Commercial electrofiltration systems are developed and available on market today, and have been used to process refinery feed such as FCC bottom slurry oils and lubricant or hydraulic oils. Electrofiltration has advantages over other separation techniques. It does not have moving parts so it is reliable and simple to operate. It is also inherently energy-efficient because of the selective interaction of the particulate with the electric field. However, prior art electrofiltration technologies are effective and efficient to remove solid matters only when feeds are largely free of water. The presence of water in the feed can cause operation failure of those systems and/or significantly reduce the separation efficiency, which greatly limits their commercial value because most of the hydrocarbon liquids do contains various amount of dispersed water. For example, the oils produced from a reservoir almost always contains substantial amount of water even after water separation. Water are often used to process oils such as bitumen extraction from oil sands, de-salting of crude in refineries, steam stripping processes in chemical plants. The processed hydrocarbon liquids are inevitably left with residual of the water. Prior art solutions to the problem of dispersed water in electrofiltration techniques generally involve removing water from the hydrocarbon by such processes as heat drying, air stripping, absorption removal, gravity separation, or centrifugal separation. These methods generally add significant cost to electrofiltration methods, thereby defeating the low-cost and low energy advantages of electrofiltration technology. There is a need for an improved electrofiltration technology that allows processing the feed in the presence of dispersed water.
U.S. Pat. No. 8,114,274 describes a method for treating bitumen froth with high bitumen recovery and dual quality bitumen production. The method includes using multiple gravity settling steps to separate phases containing bitumen in a hydrocarbon diluent from phases containing water, fine solids, and residual bitumen. Naphtha is provided as an example of a hydrocarbon diluent. One described advantage of the method is generation of a lighter bitumen stream that is suitable for transport by pipeline without further processing.
U.S. Published Patent Application 2012/0000831 describes methods for separating out a solvent feed after use in recovery of bitumen from oil sands. The method includes treating a bitumen froth with a paraffinic or naphthenic type diluent to produce bitumen and froth treatment tailings. Toluene is identified as a naphthenic type diluent that can improve bitumen recovery from tailings.
U.S. Published Patent Application 2014/0021103 describes methods for extracting bitumen from an oil sand stream. The method includes contacting the oil sand stream with a non-aqueous solvent and then screening the combined oil sand and solvent stream to form a screened oil sand stream and a rejects stream. Bitumen is then extracted from the screened oil sand stream.
U.S. Pat. No. 5,308,586 describes an electrostatic separator using a bead bed. The separator is described as being suitable for separating FCC catalyst fines from an FCC slurry oil. The electrostatic separator is periodically backflushed with additional treated slurry oil to remove particles from the separator. These backflushed particles are returned to the FCC reactor.